Polypropylene (including ethylene-propylene block copolymers) has excellent characteristics and is relatively inexpensive, and hence, has been widely used in automobile outer plate materials and interior trim materials. However, the wall-thinning of a polypropylene molded article is now proceeding as the molded article has been made large in size and light in weight.
Therefore, a high rigidity polypropylene excellent in rigidity and impact resistance has been desired.
The present situation is that when a high melt-fluidity polypropylene has been produced by polymerization, the polypropylene is very brittle and there has not been obtained such a polymer as to withstand the practical use. On the other hand, as a method of improving the melt-fluidity, there has been known a method which comprises adding a small amount of an organic peroxide to a low melt-fluidity polypropylene or its composition and heat-treating the mixture. However, the polypropylene obtained by such a method is remarkably low in rigidity and, in addition, has a problem of an odor due to the heat-treatment and in addition such a problem that a flow mark is caused on the surface of an injection molded article, or the like. Accordingly, it has been strongly desired to develop a polypropylene excellent in rigidity, impact strength, melt-fluidity and the like without requiring such a heat treatment.